Question about CO2 scrubbers effect

[reefkeeper2]

I have been using a recirculating scrubber at night for a few weeks now and it has definitely raised my nighttime pH. I wanted to see if it could boost my daytime pH as well and found it has no effect at all. The pH of the water going into the skimmer is 8.1 and the pH coming out is the same 8.1. Is there a limit to the CO2 removal ability? The media is new. The skimmer is a BubblKing 250 internal.

 

[fryman]

The limiting factor is usually air flow. I've used a large air pump and air stones to peg pH at 8.3 but found that the amount of soda lime this consumes can become cost-prohibitive. But I can use the setup with a controller to peg pH pretty much wherever I want.

 

[reefkeeper2]

I was just wondering if there was something wrong with the media. Shouldn't the water exiting the skimmer have a higher pH even if it starts out at 8.1?

 

[Andresnyc93]

A lot of the times is not an equipment issue, it’s a ventilation issue in your home. Specially if tank isn’t getting some fresh air it’s hard to keep the ph stable. I find that if you run your air intake to the outside you’ll have greater chances of having a better ph but the Co2 scrubber can only scrub so much if there isn’t fresh air in the room.

 

[MichaelReefer]

I mean, it wont raise your PH forever, so yes it has a limit. I run one 24/7 and My PH normally spikes to 8.4 during the day and falls to 8.15-8.2 at night.

 

[reefkeeper2]

A lot of the times is not an equipment issue, it’s a ventilation issue in your home. Specially if tank isn’t getting some fresh air it’s hard to keep the ph stable. I find that if you run your air intake to the outside you’ll have greater chances of having a better ph but the Co2 scrubber can only scrub so much if there isn’t fresh air in the room.

I don't think I'm getting my point across. If the pH of the water going into the scrubber is already at 8.1, shouldn't the pH of the water coming out of the scrubber be higher than 8.1? Is there an upper limit to how much CO2 a recirculating scrubber can remove? The reason I'm asking is that I question if my media (which is new) might be substandard or already partially exhausted. I would expect the pH of the water exiting the skimmer to be a few points higher than the water going in. I suppose if the water going into the skimmer was at 7.9, I would see a bigger difference. Once the pH gets above 8 there is not so much of an effect. If this is so, there is really no reason to run a scrubber 24 hours a day.

 

[Randy Holmes-Farley Verified Community Expert]

I was just wondering if there was something wrong with the media. Shouldn't the water exiting the skimmer have a higher pH even if it starts out at 8. We

It’s not as simple as that.

The scrubber is removing CO2, not eliminating it.

Let’s say the air has 800 ppm CO2 and the effluent air has 400 ppm CO2.

seawater at 7 dKH and pH 7.8 will have its pH raised by aeration with 400 ppm CO2 air, but the same water at pH 8.1 will have its pH unchanged, and the same water at pH 8.4 will haves its pH lowered.

That’s just a random example, but it shows the complexity.

 

[fryman]

Sure there are plenty of factors and interactions for a chemist to consider However, from this humble engineer's point-of-view, a sufficiently powerful scrubber in recirculating mode will remove CO2 from the water, and thus increase pH. This particular aspect doesn't seem very complex to me.

If you have a sufficiently large airflow circuit through CO2-absorbing media and bubbling in your aquarium water (via skimmer or air stones), pH will rise. The amount it rises is difficult to predict, but if you want pH to rise more than any particular scrubber provides, the most effective way I found to do so is increased airflow.

Ambient air, livestock respiration, and possibly other processes add CO2 and thus counter-act the scrubber. Most people use a skimmer to provide the scrubber airflow, which in my testing wasn't the most powerful way to use a CO2 scrubber. But it works to some degree and is enough to get a boost to pH for most who try it.

 

[Randy Holmes-Farley Verified Community Expert]

Sure there are plenty of factors and interactions for a chemist to consider However, from this humble engineer's point-of-view, a sufficiently powerful scrubber in recirculating mode will remove CO2 from the water, and thus increase pH. This particular aspect doesn't seem very complex to me.

It is complex. You are simple stating what a device of assumed efficacy can attain. What if “sufficiently powerful” devices do not describe ordinary scrubbers and skimmers?

 

[Joe31415]

If the pH of the water going into the scrubber is already at 8.1, shouldn't the pH of the water coming out of the scrubber be higher than 8.1?

Have you considered it is coming out at a higher pH, but not enough higher for your equipment to notice the difference?
For example, if whatever you're testing with can give you pH with a resolution of .1. If your water enters the skimmer at 8.112 and leaves at 8.119, the display is going to read 8.1 for both samples even though the second one is higher.

IME, once the scrubber is hooked up (or turned on or the media is replaced), going from 8.1 to 8.3 can take about a day. It's certainly not something you're going to notice in the amount of time it takes the water to pass through the skimmer. I'm not sure you're going to be able to measure such a minute change in pH with hobby grade equipment.

TLDR, maybe each time the water passes through the skimmer it's pH goes up by .0001. You're not going to be able to measure it until it's gone through enough times that all those .0001 bumps start adding up.

 

[fryman]

It is complex. You are simple stating what a device of assumed efficacy can attain. What if “sufficiently powerful” devices do not describe ordinary scrubbers and skimmers?

I'm in agreement with you on the complexity, and perhaps the OP was simply looking to understand why the tank pH behaves as it does. If so then I defer to your expertise on the matter. I was only offering my experience in case the OP was looking to increase pH with a scrubber.

But *if* the OP is looking for higher pH from a scrubber, I'm suggesting to look at the skimmer's airflow. You may be able to adjust the skimer airflow significantly, many nowadays have a valve that does this very thing. If this still won't do the trick, either accept the setup's limit or get an air pump.

i believe @Randy Holmes-Farley is right, and "sufficiently powerful" often does not describe what people are using - skimmers with ~10l/min airflow - which probably won't hit 8.3+ pH. However I did not find it very difficult (or expensive) to increase airflow with an air pump and it was many times more powerful than my skimmer (which maxes out at 11 liters/min)

I'm using a 100l/min air pump with fine pore diffusers and this on a scrubber was able to raise pH to 8.3+ under any conditions I tested; day or night, and even with 1000+ ppm ambient CO2. I think that would be overkill for the OP's case. I only run mine a few hours per day. But something smaller would definately be feasible.

 

[reefkeeper2]

It’s not as simple as that.

The scrubber is removing CO2, not eliminating it.

Let’s say the air has 800 ppm CO2 and the effluent air has 400 ppm CO2.

seawater at 7 dKH and pH 7.8 will have its pH raised by aeration with 400 ppm CO2 air, but the same water at pH 8.1 will have its pH unchanged, and the same water at pH 8.4 will haves its pH lowered.

That’s just a random example, but it shows the complexity.

This makes some sense to me because this is what I've observed. It's the fact that the scrubber is recirculating and not using the ambient room air that makes it confusing to me.

 

[smalltanks]

I'm in agreement with you on the complexity, and perhaps the OP was simply looking to understand why the tank pH behaves as it does. If so then I defer to your expertise on the matter. I was only offering my experience in case the OP was looking to increase pH with a scrubber.

But *if* the OP is looking for higher pH from a scrubber, I'm suggesting to look at the skimmer's airflow. You may be able to adjust the skimer airflow significantly, many nowadays have a valve that does this very thing. If this still won't do the trick, either accept the setup's limit or get an air pump.

i believe @Randy Holmes-Farley is right, and "sufficiently powerful" often does not describe what people are using - skimmers with ~10l/min airflow - which probably won't hit 8.3+ pH. However I did not find it very difficult (or expensive) to increase airflow with an air pump and it was many times more powerful than my skimmer (which maxes out at 11 liters/min)

I'm using a 100l/min air pump with fine pore diffusers and this on a scrubber was able to raise pH to 8.3+ under any conditions I tested; day or night, and even with 1000+ ppm ambient CO2. I think that would be overkill for the OP's case. I only run mine a few hours per day. But something smaller would definately be feasible.

Thank you for your response to this thread, it is exactly the information I was looking for.
I’m currently using an el cheapo 1L/min air pump with a lime wood airstone and saw no effect on ph. I was considering getting a schego 100L/min pump, but not sure if upgrading pump size was the best way to go. From your response and others it seems to be the best method. I also didn’t know fine pore diffusers existed, so thank you very much for that information also.
i live in a small apartment with my girlfriend so our ambient CO2 would easily be over 1000ppm. There’s no windows to open, only 2 huge sliding doors to the balcony so unfortunately getting air from outside is not feasible for at least 50% of the year.
I’ll be replicating your set up (what I was considering doing anyways) and hopefully my ph goes from a usual 7.6 (terrible I know) to 8.0+.